Methods for developing electrostatic images

ABSTRACT

Development means and method for developing electrostatic images in a moving insulating surface with developer material in which the flow of the developer material onto the insulating surface is such that a dynamic developer crown is created of such a size to substantially develop the electrostatic image. Preferably the means for creating the developer crown is a developer receptacle positioned in near contact with the moving insulating surface.

United States Patent [191 Hider et a1.

[ Jan. 15, 1974 METHODS FOR DEVELOPING ELECTROSTATIC IMAGES Inventors: Theodore M. Hider; Frank A.

Hawn; George E. Makie, all of San Jose, Calif.

International Business Machines Corporation, Armonk, N.Y.

Filed: July 1', 1971 Appl. No.: 158,811

Assignee:

U.S. Cl 117/175, 118/636, 118/637, 222/D1G. 1

Int. Cl G03g 13/08 Field of Search 117/17.5; 118/636, 118/637; 222/D1G. l, 415; 355/3, 17

References Cited UNITED STATES PATENTS 8/1955 Young 117/l7.5 10/1963 Lehmann et a1 1 ll7/17.5

3/1964 Olden ll7/l7.5 9/1964 Carlson l17/17.5

3,220,303 11/1965 Stowell l17/17.5 3,223,548 12/1965 Clark et a1. 117/l7.5 3,462,285 8/1969 Thompson 117/l7.5 3,666,518 5/1972 Luttman et a1. 117/17.5 3,536,042 10/1970 Weller 118/637 3,550,555 12/1970 Hudson 118/637 3,672,330 6/1972 Sato et a1 118/637 Primary ExaminerWilliam D. Martin Assistant ExaminerM. Sofocleous 5 7 ABSTRACT Development means and method for developing electrostatic images in a moving insulating surface with developer material in which the flow of the developer material onto the insulating surface is such that a dynamic developer crown is created of such a size to substantially develop the electrostatic image. Preferably the means for creating the developer crown is a developer receptacle positioned in near contact with the moving insulating surface.

6 Claims, 1 Drawing Figure INVENTORS THEODORE M. HIDER FRANK A HAWN GEORGE E. MAKIE ATTORNEY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electrostatography and, more particularly, relates to novel development means and methods for developing electrostatic images. 7

2. Description of the Prior Art In an electrostatographic process known as electrophotography, an electrostatic latent image is formed on a photoconductive insulating member and is developed or made visible by the attraction thereto of finely divided pigmented material, commonly known as toner. One prior art development method for rendering the electrostatic image visible is known as parallel flow cascade development in which a developer material is poured or cascaded over the surface of the photoconductive insulating member, while it is moving in a parallel direction with the developer material. This developer material contains a mixture of particles known in the art as carrier and much smaller pigmented powder particles or toner which are charged by and electrostatically adhere to the carrier particles. As the developer mixture cascades over the electrostatic latent image on the surface of the photocondctive insulating member, the toner particles are attracted to the electrostatic image from the carrier particles and deposited on the photoconductive insulating member to render the electrostatic latent image visible.

In parallel flow development, the velocity of the cascading development material must exceed the velocity of the moving photoconductive member for high quality image development. With this type of development, an individual electrostatic charge on the member will be contacted by a number of carrier particles full oftoner powder for transfer thereto. However, as the velocity of the photoconductive member is increased to higher rates of speed, the velocity of the photoconductive member now will exceed the velocity of the developer material if it is merely dropped on the member so that the same individual electrostatic charge will be contacted by carrier particles which are substantially toner depleted because the carrier particles will have previously contacted other electrostatic charges and will have given up substantially all of their toner. In this latter situation, image density of the resultant toner image falls off and other forms of image degradation appear.

Moreover, if the photoconductive member is in the form of a drum or cylinder and the diameter of the drum is decreased, the above effects show up at lower velocities because the electrostatic image is in contact with the developer material for a shorter period of time. Furthermore, there is an upper limit in velocity that the developer material can exceed the velocity of the photoconductive member because, in the known parallel flow development method, the development of the electrostatic image begins at the point of entry of the developer material onto the photoconductive member and completed at a point distant from the entry of the development material. Thus, the carrier particles are in a toner depleted state as they leave the developed image, and if their velocity is sufficiently high, they will scrub off or remove portions of the developed image, thereby degrading th image quality.

Another type of development system is one in which the photoconductive member is moved through a bath of developer material. This type of system offers the advantage of essentially eliminating the inherent abrasion or sandblast effect of cascade development, which is caused by high velocity developer material contacting the moving photoconductive member. However, such a system complicates the replenishment of toner particles taken out of the system by the developed electrostatic image.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide novel development means and methods which are capable of very high speed development of electrostatic images, and yet which produce high quality toner images.

Another object of the present invention is to provide novel development means and methods which are capable of such high speed development without degradation of the finished toner image.

Another object of the present invention is to provide development means and methods which eliminate the abrasion problems at ,high speed without complicating the replenishment of the toner particles, especially when the electrostatic image carrying member is in the form of a drum.

Another object of the present invention is to provide a novel development means and method which causes high quality development of an electrostatic image independent of the surface speed of the member carrying the image.

A further object of the present invention is to provide a novel development means capable of use with an electrostatic image carrying member traveling either clockwise or counterclockwise and thereby permit more flexibility in machine design.

The foregoing objects are achieved by a development method which creates a dynamic developer crown on the electrostatic image carrying member at such a position to direct a normal force toward the member and of such a size to substantially develop with toner particles the electrostatic image. Preferably, the means for creating the developer crown is a developer receptacle or hopper positioned in near contact with the electrostatic image carrying member. The hopper is formed with an exit aperture of a size such that, when the hopper contains a mass or head of developer material and the electrostatic image carrying member is not moving, the developer material does not exit the aperture. The formed developer crown is substantially wider than the aperture extending on both sides thereof and takes on a dynamic condition when the electrostatic image carrying member is moved.

DESCRIPTION OF THE DRAWING The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawing of which:

The FIGURE is a schematic view of an embodiment of the development means of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the FIGURE, there is partially shown a moving member 11 having an insulating surface l2 carrying an electrostatic charge pattern. Preferably, the member ll comprises a photoconductive layer and the electrostatic charge pattern is formed by uniformly electrostatically charging the surface 12 by conventional corona discharge charging means (not shown) and exposing the photoconductive layer to a light image from a light source (not shown), either indirectly as reflected from a document or directly from a cathode ray tube. However, a photoconductive layer is not required and the electrostatic charge pattern can be se lectively deposited by charging means, such as a pin tube, known in the art.

For developing the electrostatic charge pattern carried on the member ll, a development system or station 13 is provided and employs the novel development means and methods of the present invention. The station l3 comprises means for providing a flow of developer material 14 which is a mixture of carrier particles and toner powder which electrostatically adheres to the carrier particles. The developer material M is carried upwardly from a reservoir (not shown) to the receptacle 15 via known conveyer means such as a feed screw or conveyer buckets 16.

In accordance with the present invention, the development station 13 must include means for creating the developer crown 18 from the point of entry of the developer material onto the surface 12 of the member and on both sides of this point of entry. In the embodiment shown in the FIGURE, the creation and maintenance of the developer crown are accomplished in the following way. The receptacle 15 is formed with an aperture 17 of a predetermined size and is in spaced relation with the surface 12 such that when the surface 12 is stationary, the developer material 14 will not flow out of the aperture and will form a developer crown 18.

It will be understood that the mass or head of developer material necessary to maintain a no-flow condition when the surface 12 is stationary will vary depending on the particle size of the carrier particles and the weight of these particles, i.e., sand core versus iron core.

With this embodiment of the developer means, as herein described, the member ll carrying the electrostatic image is moved in a counterclockwise direction into the uppermost edge 19 of the developer crown 18 which, because of the movement of the drum ll, has been placed in a dynamic condition and there is a flow of developer material from the receptacle 15 into and out of the developer crown 118. Due to this dynamic action of the development crown, the electrostatic image carried on the surface 12 of the member 11 is substantially developed by the time it leaves the lowermost edge 20 of the developer crown.

While the embodiment of the FIGURE has shown the position of the receptacle 15 to be at an angle of about from the vertical, it will be understood that the invention is meant to include the creation of the development crown 18 at a point anywhere between about zero degrees and about 60 to the vertical. It will be recognized that the parameters of aperture size, spacing between the receptacle and the surface 12 of the member ll, and the head of developer material will have to be adjusted accordingly when the development crown is to be created at a different angle than shown in the FIG- URE. It also will be recognized that these same parameters will be influenced by the direction of movement of the member H. For example, the development crown is more esily formed at a larger angle when the member 11 is moving in a clockwise direction. in addition, while an angle of about 5 is preferred when the member 11 is moving in a counterclockwise direction, a larger angle such as 45 is preferred when the mem' ber ll is moving in the counterclockwise direction because of a carry-out problem. That is, the development crown can be created at about 5 with a counterclockwise direction and the fur seal 21 is sufficient to prevent the developer material from being carried out of the developer station 13. However, when the member ll is moving in a clockwise direction, the carry-out of the developer material becomes somewhat of a prob lem with the developer crown created at such a small angle as 5.

The following example further specifically defines the present invention in respect to a method of developing electrostatic images with a developer crown.

EXAMPLE I A drum carrying a photoconductive layer as described in US. Pat. no. 3,484,237 was charged with a uniform electrostatic charge from a corona unit to a surface potential of about 600 volts and exposed to a line image to form a latent electrostatic image on its surface. The drum was then rotated in a counterclockwise direction, through the developer station as shown in the FIGURE, containing a commercially available developer material. With the receptacle positioned at about 5 to the vertical, the aperture of the receptacle was three-fourths inch, the spacing between the bottom of the receptacle and the photoconductive surface was three-eights inch and the head of the developer material in the receptacle was 6 inches high. The developed copy was excellent at a rotational speed of 24 inches per second. Moreover, without making any adjustments to the developer station, the rotational speed was increased to a speed as high as 50 inches per second with no substantial change in the quality of the developed copy. Further, development was shown to be possible at inches per second.

As can be seen from the foregoing example, the development method of the present invention has the inherent advantage of having a self regulating developer flow. That is, once the developer crown has been established for one development speed (i.e., the movement of the electrostatic image through the developer crown) such as a slow 8 inches per second, the development speed can be increased and the flow rate automatically adjusts to the increased speed, such as 50 inches per second. Thus, this method of development is essentially speed insensitive.

However, it will be recognized that as the speed of the electrostatic image carrying member is charged, the conveyor system delivery rate may either be automatically changed proportionally or an overflow path may be provided in the receptacle so as to maintain an optimum head of developer material in the receptacle. In addition, it will be recognized that the toner replenish ment rate should be changed inasmuch as this rate is proportional to the number of images developed per unit of time. This change, again, can easily be accomplished automatically, such as, synchronizing the toner dispenser in the system with the drive motor of the member carrying the electrostatic image. Alternatively the toner concentration can be sensed and the toner replenishment rate automatically adjusted accordingly. This self regulating advantage permits the design of a dual speed machine which can function both as a low speed facsimile printer or as a high speed computer output printer.

While the invention has been shown and described with reference to preferred embodiments thereof, it will be appreciated by those skilled in the art that variation in form may be made therein without departing from the spirit and scope of .the invention.

What is claimed is:

1. In an electrostatographic method comprising the steps of forming an electrostatic image on an insulating surface, and developing said electrostatic image by providing a continuous uniform flow of developer material, comprising a mixture of carrier particles and toner powder, from a developer material source onto said insulating surface, while said insulating surface is moving, to render it visible, wherein the improvement comprises:

creating and maintaining a dynamic crown of developer material on said moving insulating surface at the point the material flows onto said surface and with a force normal to the surface by positioning said source of developer material in a predetermined spaced relationship with the insulating surface, said crown being non-dynamic when the flow of developer material from the developer material source is stopped and becoming dynamic due to the continuous uniform flow of developer material and the movement of the insulating surface, and being of a size such that the electrostatic image is substantially developed while passing through said dynamic developer crown.

2. The electrostatographic method of claim 1 in which the point of the developer crown is about 0 to about from the vertical.

3. The electrostatographic method of claim I in which said developer crown still exists but becomes non-dynamic and stationary when said insulating surface is stopped.

4. The electrostatographic method of claim 2 in which the point of the developer crown is about 5.

5. The electrostatographic method of claim 1 in which the step of creating the developer crown is caused by restricting the flow of developer material onto said surface.

6. The electrostatographic method of claim 5 in which the restriction of the developer flow is assisted by the mass of the developer material above the developer crown. 

2. The electrostatographic method of claim 1 in which the point of the developer crown is about 0* to about 60* from the vertical.
 3. The electrostatographic method of claim 1 in which said developer crown still exists but becomes non-dynamic and stationary when said insulating surface is stopped.
 4. The electrostatographic method of claim 2 in which the point of the developer crown is about 5*.
 5. The electrostatographic method of claim 1 in which the step of creating the developer crown is caused by restricting the flow of developer material onto said surface.
 6. The electrostatographic method of claim 5 in which the restriction of the developer flow is assisted by the mass of the developer material above the developer crown. 